As described in U.S. Pat. No. 3,775,968, for example, and elsewhere, it is known to use an escapement for watches in which an inverse lever constitutes the stepping device.
Two main problems are encountered with conventional stepping mechanisms. Firstly, the main driving force may intermittently release the oscillatable lever and hence it is necessary to provide stable end positions of the lever. Secondly, it is frequently found that misses or undesirable releases of the wheel can occur at the moment of impulse so that the escapement wheel carries out a reciprocating motion instead of a unidirectional rotation.
The first problem has been solved by the use of permanent magnets built into the watch movement and a magnet carried by the lever. The interaction between the two types of magnets serves to lock the lever at the ends of its oscillation stroke.
The second problem has been solved variously, e.g. by the use of braking springs which act upon the shaft of the drive wheel. In a second solution, moveable pallets are resiliently biased by a spring on the lever and are displaceable in respective slots in a plane parallel to the plane of lever. This system allows the pallets to engage the wheel even during the impulse but also permits release of the wheel as required for the stepping motion.
The first approach has some disadvantages as are discussed in the above-mentioned patent whereas the second approach creates difficulties with respect to fabrication of the pallets and the resilient means.